Self-shielded Di/Dt transformer for a meter

ABSTRACT

A sensor includes a core, first and second windings, an integrating amplifier circuit and a DC stabilization circuit. The first and second windings are wrapped around the core. The integrating amplifier circuit has a first input coupled to receive a sensed current from the first winding, and an output operably coupled to provide a current the second winding. The integrating amplifier circuit is configured to generate a phase shift from an input current received at the first input and the current provided to the second winding. The DC stabilization circuit includes a first resistive path coupled between the output of the integrating amplifier circuit and the first input of the integrating amplifier circuit, and a second resistive path coupled between the first winding and the first input of the integrating amplifier circuit.

This application is a continuation of U.S. patent application Ser. No.14/274,144, filed May 9, 2014, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/821,503, filed May 9, 2013,both of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to electricity measurements, andmore particularly, to current measurements such as those carried out inan electricity meter.

BACKGROUND

One of the goals of electricity metering is to accurately measure theuse or consumption of electrical energy resources. With suchmeasurements, the cost of generating and delivering electricity may beallocated among consumers in relatively logical manner. Another goal ofelectricity metering is help identify electrical energy generation anddelivery needs. For example, cumulative electricity consumptionmeasurements for a service area can help determine the appropriatesizing of transformers and other equipment.

Electricity metering often involves the measurement of consumed power orenergy in the form of watts or watt-hours. To this end, meters includevoltage sensors and current sensors that detect, respectively, thevoltage and current delivered to the load. In most cases, the purpose ofthe voltage sensor is to provide a measurement signal that represents ascaled version of the voltage waveform delivered to the load. Similarly,a current sensor provides a measurement signal that represents a scaledversion of the current waveform delivered to the load.

The current measurement in a utility meter can be challenging because ahigh accuracy is required, and common current sensor technologies can besusceptible to various sources of error. Present metering technologiesinvolve current transformers, or CTs. Existing CT designs are prone tosaturation and may distort causing error especially in a DC magneticfield or with a half wave rectified load. To compensate for such errors,additional circuitry is often required, which increases costs.Alternatively, other costly steps must be taken to avoid errors. Forexample, in a CT, it is important that certain windings around the CTcore have the exact same number of turns. This requirement makes themanufacture of the specialized metering CT complex and expensive.

There is a need, therefore, for a current sensor arrangement thatfavorably improves upon one or more of shortcomings of existingtransformers, for example, by providing sufficient accuracy undervarious circumstances while reducing production cost.

SUMMARY OF THE INVENTION

The invention addresses the above-describe needs, as well as others, byproviding a sensor that may be used in a utility meter that includesfeatures described herein.

A first embodiment is a sensor includes a core, first and secondwindings, an integrating amplifier circuit and a DC stabilizationcircuit. The first and second windings are wrapped around the core. Theintegrating amplifier circuit has a first input coupled to receive asensed current from the first winding, and an output operably coupled toprovide a current the second winding. The integrating amplifier circuitis configured to generate a phase shift from an input current receivedat the first input and the current provided to the second winding. TheDC stabilization circuit includes a first resistive path coupled betweenthe output of the integrating amplifier circuit and the first input ofthe integrating amplifier circuit, and a second resistive path coupledbetween the first winding and the first input of the integratingamplifier circuit.

Another embodiment is a sensor that includes a non-magnetic core, firstand second windings, an integrating amplifier circuit and a DC balancingcircuit. The first and second windings are wound around the core. Thesecond winding operably is coupled to influence a current in the firstwinding. The integrating amplifier circuit has a first input coupled toreceive a sensed current from the first winding, and an output operablycoupled to provide a current the second winding. The integratingamplifier circuit is configured to generate a phase shift from an inputcurrent received at the first input and the current provided to thesecond winding. The sense resistor is operably coupled to receive ameasurement output current from the second winding and to convert themeasurement output current to a measurement voltage.

Another embodiment is an arrangement for use in an electricity meterthat includes a current coil configured to provide current to a load,and a sensor similar to that described above.

The above described features and advantages, as well as others, willbecome more readily apparent to those of ordinary skill in the art byreference to the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of an exemplary meter that may beused in one or more embodiments of the present invention;

FIG. 2 shows a schematic block diagram of an exemplary current sensoraccording to a first embodiment of the invention that may be used in themeter of FIG. 1;

FIG. 3 shows an exemplary embodiment of a coil that may be used in thecurrent sensor of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment of a polyphase electricity meter 10in which an arrangement according the invention is implemented.Referring to FIG. 1 specifically, the meter 10 is an apparatus formeasuring energy consumption that includes a scaling circuit 110, ananalog-to-digital conversion (“ADC”) circuit 114, a processing circuit116, a communication circuit 118, an optional display 120 and a datastore 112. As will be discussed below, the scaling circuit 110 includesat least one current sensor 200 that operates as a self-shield di/dtsensor according to at least one embodiment of the present invention.All of the elements listed above are preferably supported by a meterhousing 113, which may take a plurality of known forms. Thecommunication circuit 118, which is also optional, may be disposedwithin an interior of the meter housing 113 like the other devices, ormay be affixed to the outside of the meter housing 113.

In the embodiment described herein, the scaling circuit 110 and the ADCcircuit 114 are collectively arranged to generate digital signalsrepresentative of line voltage waveforms V_(A), V_(B), V_(C) for each ofthree phases A, B, C of a four-wire delta electrical system and otherdigital signals representative of at least three of the four linecurrent waveforms I_(A), I_(B), I_(C) and I_(N) of the four-wire deltaelectrical system. It will be appreciated, however, the meter 10 mayreadily be configured for a three-wire delta electrical service, as wellas other types of electrical service, and still employ the inventivecurrent sensor circuitry disclosed herein. In any event, the digitalsignals are typically sequences of digital samples representative of aninstantaneous voltage or current measurement on one phase with respectto either neutral or another phase. Circuits capable of generating suchsignals are known in the art.

The processing circuit 116 is configured to calculate one or more energyconsumption values based on the digital signals. The energy consumptionvalues may be communicated to a remote device using the communicationcircuit 118, displayed using the display 120, stored in the data store112, or preferably some combination of the foregoing. In accordance withthe embodiments described herein, the processing circuit 116 is furtheroperable to perform any or all of the energy consumption relatedcalculations typical for an electricity meter.

In a further detailed description of the meter 10 of FIG. 1, the scalingcircuit 110 comprises one or more current sensors 200 and voltagesensors 124. The voltage sensors 124, which may, for example, includevoltage dividers, generate a scaled down version of the voltage waveformpresent on phases of the power lines 12. The current sensors 200 arecircuits and elements that generate a voltage or current signal that isa scaled down version of the current waveform present on the phases ofthe power lines 12. In accordance with at least one embodiment of thepresent invention, each of the current sensors 200, one for each phaseA, B and C, may have the structure shown in FIG. 2.

The ADC circuit 114 includes one or more analog-to-digital convertersthat convert the scaled measurement signals into digital voltage andcurrent measurement signals. Many circuits capable of generating digitalvoltage and circuit waveform signals are well known in the art. Suitableexamples of analog to digital conversion circuits having suchcapabilities are described in U.S. Pat. No. 6,374,188; U.S. Pat. No.6,564,159; U.S. Pat. No. 6,121,158 and U.S. Pat. No. 5,933,004, all ofwhich are incorporated herein by reference. Moreover, the ADC circuit114 may readily be a part of an integrated metering chip package, aswill be discussed below.

The processing circuit 116 is a device that employs one or moreprocessing devices such as microprocessors, microcontrollers, digitalsignal processors, discrete digital circuits and/or combinationsthereof. As mentioned above, the processing circuit 116 is operable togenerate energy consumption data based on the digital signals. In oneexample, the processing circuit 116 generates watt-hour informationbased on an accumulation of products of contemporaneous voltage andcurrent samples. For example, true watt-hours for a particular phase maybe calculated as the vector product of the current waveform and thevoltage waveform. This vector product may be carried out with sampledvoltage (V_(n)) and sampled current (I_(n)) by the formula:Whrs=ΣV _(n) *I _(n)  (3)where Whrs is an accumulated energy value (i.e. watt-hours) for a timeframe from a starting time n₀ to a time corresponding to n.

Various processing circuits operable to generate energy consumption datafrom digital voltage and digital current measurement signals are wellknown in the art. Suitable examples of such circuits are described inU.S. Pat. No. 6,374,188; U.S. Pat. No. 6,564,159; U.S. Pat. No.6,121,158 and U.S. Pat. No. 5,933,004. However, in one preferredembodiment, the processing circuit is (or includes) a processing elementof a metering integrated circuit chip such as the Teridian 71M6533measurement chip (available from Maxim). In that embodiment, both theADC circuit 114 and the processing circuit 116 are disposed within thesame semiconductor package.

The processing circuit 116 is further operable to store the plurality ofenergy consumption values in the data store 112. In some embodiments,the processing circuit 116 may store energy consumption values for eachof plurality of time periods, in order to allow analysis of energy usageat different times of day, days of the week or month, or evenseasonally. The storage of consumption indexed to time periods is oftenreferred to in the industry as “load profiling”. The data store 112 maysuitably be a random access memory, EEPROM, other memory, or acombination of several types of memory. In still other embodiments, thedata store 112 may include a circular buffer, FIFO device, or othermemory that stores data in the order in which it is received. Otherknown methods may be used. In at least some embodiments, the data store112 includes memory located within the integrated chip package thathouses the processing circuit 116. The data store 112 also includes asoftware program that is executed by the processing circuit 116 toperform the operations of the processing circuit 116 described herein.

The communication circuit 118 is a device that is in some embodimentsconfigured to communicate data between the metering unit 12 and one ormore remote devices. In a system such as that shown in FIG. 1, thecommunication circuit 118 would be operable to communicate directly orindirectly with a data collection system of a utility service provider.Several of such systems are known. The utility service provider thenuses the collected data to generate billing information and/or dataforecasting information as is known in the art. To this end, thecommunication circuit 118 may suitably include a radio, a telephonemodem, a power line carrier modem, or other known communication deviceconfigured for use with utility meters. Radios may be used that operatein the 100 MHz to 1 GHz range. However, other devices may operate in thekHz or low MHZ range.

In addition or in the alternative, the communication circuit 118 isconfigured to communicate with a locally coupled device, such as aportable computing device. The communication circuit 118 may include anoptical or electrical data port, not shown, for this purpose.

The meter display 120, which is optional, may be a digital display suchas a liquid crystal display. It will be appreciated that the exactnature of the display is not particularly important to theimplementation of the invention. Nevertheless, there is an advantage ofincluding at least some display capabilities. LCD displays, moreover,have been found to have a particularly advantageous set of qualities foruse in electronic meters.

FIG. 2 shows a schematic diagram of a current sensor 200 according tothe invention as well as a black-box representation (i.e. equivalentcircuit) of a single phase of a power line 12. The power line 12equivalent circuit is represented herein as a current source I1, a highimpedance to ground resistor R1, and a coil L1. The coil L1 represents acurrent coil normally found in a utility meter that carries all (or alarge proportion) of the current delivered to a customer load on thepower line 12.

In this embodiment, the current sensor includes a first secondarywinding L2, a second secondary winding L3, both of which are wrappedaround a core, not shown on FIG. 2. The core may be permeability ofgreater than 1, as in an iron-based core, or could have permeability ofapproximately 1, such as in a Rogowski coil. In general, the windingsL1, L2 and L3 are arranged in a transformer type arrangement. To thisend, the windings L2 and L3 may cooperate with a suitable core to form atoroid (wrapped around a toroidal core) through which the first winding,often a single turn winding, passes. However, the transformerarrangement may take other forms.

By way of example, FIG. 3 shows a representative diagram of the windingsL1, L2 and L3 arranged as a transformer 302 for sensing current on thepower line 12. In this embodiment, the windings L2 and L3 are arrangedas a Rogowski coil 300 that may be used in a first embodiment of thearrangement of FIG. 2. The winding L1 is arranged as a meter currentcoil 304. The meter current coil 304 is a conductive bar or otherconductive element that carries the load current of the power line 12.The Rogowski coil 300 and the current coil 304 collectively form thetransformer 302 having the windings L1, L2 and L3 of FIG. 3. In thisembodiment, the Rogowski coil 300 forms part of the sensor 200 of FIG.2.

More specifically, the Rogowski coil 300 includes a non-magnetic core316 around which is wrapped the bifilar windings L2 and L3. The core 316may take any suitable form but preferably has a central opening 318through which the current coil 304 passes, such that the windings L2, L3substantially surround the current coil 304. The current coil 304 formsthe primary winding L1 of the transformer 302, and the windings L2, L3of the Rogowski coil 300 form the secondary windings of the transformer302. It will be appreciated that the geometry of the current coil 304and the Rogowski coil 300 may take other suitable physical forms in thetransformer 302 for current sensing purposes. As discussed above, someembodiments of the transformer 302 may even employ a current coil havinga magnetic core in lieu of the non-magnetic core 316 of the Rogowskicoil 300.

Referring again to FIG. 2, the sensor 200 also includes an integratingamplifier circuit 202, a current buffer 204 and a DC stabilizationcircuit 206. In this embodiment, the sensor 202 includes a senseresistor R3 to allow the output current measurement signal Vout to be avoltage waveform readily detectable by standard voltage-sensing A/Dconverters, such as the A/D converter 114 of FIG. 1.

As discussed above, the sensor 200 in one embodiment features a singlecore, for example, the core 316 of FIG. 3, which is wound with thewindings L2, L3. The single core preferably has an opening (e.g. it is atoroidal core) through which the primary conductor L1, which is loadedwith current to be measured, passes. (See, e.g. FIG. 2). It will beappreciated that while the core may be anything from air to a highpermeability material, a higher permeability provides greatersensitivity.

The secondary winding L2 comprises the di/dt sense winding of the sensor200, and may suitably have a turns ratio of 100-2000 with respect to theprimary winding. The secondary winding L3 forms the ratio winding of thedevice, and may suitably have a turns ratio of 400 to 4000, or anothervalue. In general, the turns ratio of the winding L3 depends on therange of the ADC circuit 114 and the upper range of the input current.In other words, the turns ratio of the secondary winding L3 should besuch that it reduces the highest expected input current, plus 20%, to alevel at which the output voltage Vout is within the range of the ADCcircuit 114.

The integrating amplifier circuit 202 in this embodiment includes anoperational amplifier U1 having an integrating feedback path. In thisembodiment the integrating feedback path includes a capacitor C1 and aserially connected resistor R2. The integrating amplifier circuit 202 isconfigured to provide a 90° phase shift from input to output, and maytake other suitable forms in other embodiments. To this end, theoperational amplifier U1 includes the inverting input 212, anon-inverting input 214, and an output 216. The output 216 is coupledvia the buffer 204 to the integrating feedback path C1, R2. Morespecifically, the output 216 is coupled to provide the amplifier outputsignal to an input of the current buffer 204. The current buffer 204 isconfigured to provide current buffering to the amplifier output signalto generate a buffered output current. The output 220 of the currentbuffer 204 is operably coupled to provide a buffered output current tothe integrating feedback path C1, R2. The feedback path C1, R2 generatesa feedback signal from the buffered output signal, and is operablycoupled to provide the feedback signal to the inverting input 212 of theoperational amplifier U1. Thus, in this embodiment, the current buffer204 is coupled in series between the output 216 of the operationalamplifier U1 and the serially connected capacitor C1 and resistor R1.

In general, the op-amp U1 is configured to sense the di/dt voltages offof the winding L2 and provide a drive current to the winding L3 in orderto force the flux in the coil to zero and cancel the voltage at its owninverting input 212.

The current buffer 204 in this embodiment is a circuit that isconfigured to boost the current drive capability of the low offsetintegrating amplifier circuit. As discussed above, the current bufferinput 218 is operably coupled to receive the amplifier output signal oroutput current from the output 216 of the operational amplifier U1, andis operably coupled to provide the buffered output current to its output220. The current buffer 204 in this embodiment comprises transistors Q1,Q2, Q3, Q4, capacitors C3, C5, and resistors R5, R11 configured as a lowcost current buffer.

More specifically, the transistor Q2 is a PNP BJT having a baseconnected to the input 218, a collector coupled to a lower rail biasvoltage VEE, and an emitter. The transistor Q4 is an NPN BJT having abased connected to the input 218, a collector coupled to a higher railbias voltage VCC, and an emitter. The capacitor C3, which may suitablybe 1 μF, is coupled between the input 218 and the emitter of thetransistor Q2. Analogously, the capacitor C5, which may also be 1 μF, iscoupled between the input 218 and the emitter of the transistor Q4. Thetransistor Q1 is a PNP BJT having a base coupled to the emitter of thetransistor Q4, a collector coupled to the lower rail voltage VEE, and anemitter coupled to the output 220. The transistor Q3 is a NPN BJT havinga base coupled to the emitter of the transistor Q2, a collector coupledto the higher rail voltage VCC, and an emitter coupled to the output220. The resistor R5, which may suitably be a 10 kΩ resistor, is coupledfrom collector to base of the transistor Q3. Similarly, the resistorR11, which may also be a 10 kΩ resistor, is coupled from collector tobase of the transistor Q1. It will be appreciated that other currentdrives may be used as the current buffer 204.

In any event, the output 220 of the current buffer 204 is operablycoupled to provide the buffered output current to a first terminal 222of ratio winding L3. As discussed above, the resistor R2 and capacitorC1 also receive the buffered output signal and generate a feedbacksignal therefrom to perform integration. The resistor R2 and capacitorC1 provide the feedback signal to the non-inverting input 212.

The DC stabilization circuit 206 comprises the resistors R4, R6, R8. Theresistors R4, R6 are serially coupled between the output 216 of theop-amp U1 (via the current buffer 204) and the inverting input 212 ofthe op-amp U1. More specifically, in this embodiment, the resistors R4,R6 are coupled between the output 220 of the current buffer 204 and theinverting input 212 of the op-amp U1. Each of the resistors R4, R6 maysuitably have a resistance of 5 MΩ. The resistor R8 is coupled betweenthe di/dt winding L2 and the inverting input 212 of the op-amp 206. Theresistor R8 may suitably have a resistance of 10 MΩ.

In general, the DC stabilization circuit 206 provides DC stabilizationto the circuit. To this end, the DC stabilization circuit 206 provides aDC resistive path back to the inverting input 212 of the op-amp U1.Without out it, the op-amp U1 output would drive to the output rail ofthe op-amp U1. The resistor R8 improves DC offset to increase commonmode range. In particular, with the combination of R4 and R6, thereneeds to be an impedance to the reference point, or the signal would beshorted by the sense winding L2. The impedance of R8 compared to theinput impedance of the op-amp U1 is relatively small.

The sensor 200 also includes a DC isolation capacitor C2 coupled betweenthe output 216 of the op-amp U1 (via the current buffer 204) and thefirst terminal 222 of the ratio winding L3. In this embodiment, the DCisolation capacitor C2 is couple between the output 220 and the firstterminal 222. The DC isolation capacitor C2 prevents DC bias voltagesfrom passing between the second winding L3 and the integrating amplifiercircuit 202. In series with the capacitor C2 is a resistor R7 of 1Ω. Theresistor R7 adjusts the output impedance to stabilize the network. Inthis embodiment, the resistor R3 is used as a sense resistance whicheffectively converts the output current, which represents themeasurement current, from the winding L3 to a corresponding outputvoltage Vout. The sense resistor R3 may suitably be 1Ω in thisembodiment. The Vout output is operably coupled to the ADC 114 of FIG.1.

In this embodiment, the current measurement signal Vout is biased to anall-positive voltage using a voltage source V3 of 3.3 volts. The 3.3voltage reference VREF is provided as the reference voltage connectionto the winding L2, the non-inverting input of the op-amp U1, and thereference for the sense resistor R3. This biasing reference voltageallows the measurement signal, which represents that AC currentwaveform, to always be a positive value, even through the negativeswings of the AC cycle. In other words, instead of the measurementsignal ranging from −1.5V to 1.5V peak to peak, for example, the Voutsignal would range from 0.1 to 3.1 volts peak to peak.

In operation, the primary current on the winding L1 induces a voltage(Vsense) on the winding L2 proportional to K di/dt, where K is aconstant. “K” is a function of temperature, time, geometry, and corepermeability. The voltage Vsense is sensed by the op-amp U1. The op-ampU1 will then drive a current, via the buffer 204 (i.e. the bufferedoutput current), through the winding L3 to drive the flux of the coil tozero to reduce the difference of the voltage sensed at the inputs 212and 214 to zero. However the current produced will be proportional tothe input current (from L1) by the exact turns ratio between L1 and L3,due to the coupling of L1, L2 and L3.

The sensor 200 in normal operation will exhibit a higher accuracy over alarger dynamic range than a traditional CT, because the non-magneticcore does not have undesirable excitation currents. If, instead of aRogowski coil, the windings L2 and L3 are wrapped around a magneticcore, then Vsense will be amplified by the core material, resulting ingreater sensitivity. Such a device will be immune to AC fields unlike anembodiment employing a Rogowski coil. Moreover, because of theintegrating amplifier circuit 202, the device will be immune to DCmagnetic fields and DC currents unlike a traditional currenttransformer. Ratio accuracies better than 0.05% over the entire rangeare typically achievable. The current buffer 204 allows for a lowdriving op-amp, thereby reducing costs.

In the case where an external DC field or current causes totalsaturation, the device would be reduced to a sensor that is not unlike atraditional Rogowski coil. However, the invention still providesimprovements (as it would if the permeability was 1): immunity to errordue to shifts in inductance, due to external influences, and due toaging, and due to primary vs. coil window position.

In addition a single coil could be used with multiple primaries with noadditional error like a traditional CT. Rogowski coils exhibit animbalanced transfer function due to the mutual inductances of multipleprimaries not being equal.

The above-describe embodiments provide one or more of the followingadvantages:

-   -   1. Immunity to near AC fields under normal operation (Core        permeability>>1 only);    -   2. High DC Tolerance due to near magnetic fields or half wave        rectified loads;    -   3. Higher accuracy when compared to a traditional CT or Rogowski        coil;    -   4. Immunity to fluctuations in self/mutual inductance due to        temperature, aging;    -   5. Low cost;    -   6. Immunity to saturation within common mode range of active        circuit, recovers quickly if range exceeded;    -   7. Small and light weight;    -   8. Inexpensive materials;    -   9. Reduction in component count; and    -   10. Multiple primaries may be measured without imbalance, unlike        a Rogowski Coil.

It will be appreciated that the embodiment of FIG. 2, or a modificationthereof, may be used in a form 2S meter without measurement imbalancebetween the current coils, unlike a Rogowski coil which has been used inthe prior art. A Rogowski coil's mutual inductance changes with theposition of the primary relative to the center of the Rogowski coilwhich may result in imbalanced current measurements when multipleprimaries are used due to the heterogeneous nature of the windings.

This invention could be used in any meter, however meters that requireDC immunity and where high accuracy is required (such a 0.1% accuracyclass) are ideal cases.

Some notable features include the DC stabilization circuit 206, whichincludes the very high impedance (e.g 5000 k-ohm) series connectedfeedback resistors R4 and R8, as well as the U1 input resistance R8 of10000 k-ohm. In addition, the low-cost buffer 204 provides cost savingsover more complex designs.

It will be appreciated that the above described embodiments are merelyexemplary, and that those of ordinary skill in the art may readilydevise their own modifications and implementations that incorporate theprinciples of the present invention and fall within the spirit and scopethereof.

We claim:
 1. A sensor for use in metering, comprising: a) a core aroundwhich are wound first and second windings: b) an integrating amplifiercircuit having a first input coupled to receive a sensed current fromthe first winding, and an output operably coupled to provide a currentto the second winding, the integrating amplifier circuit configured togenerate a phase shift from an input current received at the first inputto the current provided to the second winding; and c) a DC stabilizationcircuit including a first resistive path coupled between the output ofthe integrating amplifier circuit and the first input of the integratingamplifier circuit, and a second resistive path coupled between the firstwinding and the first input of the integrating amplifier circuit.
 2. Thesensor of claim 1, wherein the integrating amplifier circuit includes anamplifier having the first input, and an integrating feedback pathcomprising a resistor and a serially connected capacitor, theintegrating feedback path operably coupled to receive the currentprovided to the second winding, and configured to generate a feedbacksignal therefrom, the integrating feedback path configured to providethe feedback signal to the first input.
 3. The sensor of claim 2,further comprising a current buffer operably coupled to receive anoutput signal from an amplifier output of the amplifier, the currentbuffer configured to buffer the output signal to generate the currentprovided to the second winding.
 4. The sensor of claim 1, furthercomprising a sense resistor operably coupled between the second windingand a reference voltage, the sense resistor configured to generate anoutput voltage representative of current received from the secondwinding.
 5. The sensor of claim 1, wherein the second winding isoperably couple to influence current in the first winding.
 6. The sensorof claim 1, further comprising a positive bias voltage source operablycoupled to provide a positive bias voltage between the first winding andthe integrating amplifier circuit, the positive bias voltage maintaininga positive voltage on the second winding at all points of an AC cycle ofthe sensed current.
 7. The sensor of claim 1, wherein the first windingand the second winding are bifilar windings.
 8. The sensor of claim 1,wherein the first resistive path and the second resistive path have asame resistance.
 9. A sensor, comprising: a) a non-magnetic core aroundwhich are wound first and second windings, the second winding operablycoupled to influence the first winding; b) an integrating amplifiercircuit having a first input coupled to receive a sensed current fromthe first winding, and an output operably coupled to provide a currentto the second winding, the integrating amplifier circuit configured togenerate a phase shift from an input current received at the first inputto the current provided to the second winding; and c) a sense resistoroperably coupled to receive a measurement output current from the secondwinding and to convert the measurement output current to a measurementvoltage.
 10. The sensor of claim 9, wherein the integrating amplifiercircuit includes an amplifier having the first input, and an integratingfeedback path comprising a resistor and a capacitor, the integratingfeedback path serially coupled from the output to the first input. 11.The sensor of claim 10, further comprising a buffer operably coupled toreceive an output signal from the amplifier, and to provide the currentto the second winding.
 12. The sensor of claim 9, wherein the senseresistor is operably coupled to provide the measurement voltage to ananalog-to-digital converter.
 13. The sensor of claim 9, furthercomprising a positive bias voltage source operably coupled to provide apositive bias voltage between the first winding and the integratingamplifier circuit, the positive bias voltage maintaining a positivevoltage on the second winding at all points of an AC cycle of the sensedcurrent.
 14. The sensor of claim 9, wherein the first winding and thesecond winding are bifilar windings.
 15. An arrangement for use in anelectricity meter, comprising: a) a current coil configured to providecurrent from a utility power line to a load; b) a core around which arewound first and second windings, the second winding operably coupled toinfluence the first winding, wherein the current coil, the core and atleast one of the first and second windings form a transformer; c) anintegrating amplifier circuit having a first input coupled to receive asensed current from the first winding, and an output operably coupled toprovide a current to the second winding, the integrating amplifiercircuit including an integrating feedback path coupled to receive thecurrent and generate a feedback signal therefrom, the integratingfeedback path configured to provide the feedback signal to the firstinput; and d) a sense resistor operably coupled to receive a measurementoutput current from the second winding and to convert the measurementoutput current to a measurement voltage.
 16. The arrangement of claim15, wherein the core includes a central opening, and wherein the currentcoil passes through the central opening.
 17. The arrangement of claim16, wherein the core is non-magnetic.
 18. The arrangement of claim 17,wherein the first and second windings are bifilar windings.
 19. Thearrangement of claim 18, further comprising an analog-to-digitalconverter operably coupled to receive the measurement voltage from thesense resistor.
 20. The arrangement of claim 19, further comprising a DCisolation capacitor operably coupled to block DC voltage propagationbetween the second winding and the output of the integrating amplifiercircuit.